Stray currents flow to the ground (into the soil of the earth) from a rail which returns traction current in a track with a DC power supply.
Normally, the rails in DC railways are used to return current. The rails are therefore insulated from the ground. This is because no current is intended to flow from the rails through the ground into surrounding conducting structures. Such structures can be parts of building foundations or tunnel systems, or else pipeline systems. The flow of current can result in corrosion of these structures, for example, if they are made of metal.
The insulation between the rails and ground can become damaged or electrically bridged in another way over the course of time, however. Thus, stray currents could flow to ground and to the structures which are at risk.
In order to be able to identify such stray current effects, proposals have already been made to install “reference electrodes” along the track. Such an electrode measures the potential in the ground below the rail. Installing such electrodes is highly involved. In addition, evaluating the measurements from the electrodes is complicated and expensive.
Proposals have also already been made to discharge possible stray currents using special devices, for example using drainage diodes, and to indicate this current if required. Such designs result in a lasting increase in the stray currents.
Proposals have also already been made to measure the voltage between the rail and the ground at a point and to indicate an increased risk as a result of stray currents if there is a discrepancy from a voltage reference value.